Surface hardening for hammermill hammers and method of forming the same



Jan. 21, 1964 H. F. EILERS 3,118,199

SURFACE HARDENING FOR HAMMERMILL HAMMERS AND METHOD OF FORMING THE SAME Original Filed Feb. 3, 1958 5 i 5 i5 7 H6. .5

United States atent Office 3,ll8,l99 Patented Jan. 21, 1954 SURFACE HARDENING FQR HAMMERMEL HAMMER?) AND METHOD OF FQRMING THE SAME Howard F. Eilers, St. Paul, Minn., assignor to Paper Calrnenson & Co., a corporation of Minnesota Griginal application Feb. 3, 1958, Ser. No. 712,732.

Divided and this application Tune 13, 1960, Ser. No.

suns

3 Claims. c1. 22 204 This invention relates to hammermill hammers of the type having one or more face portions which, when in use, are subjected to abrasive and impact forces directed longitudinally of the working face or faces. The invention also includes an improved method of forming or building up hard faces on such hammers.

in the manufacture of hammermill hammers considerations of cost are of paramount importance. The ham mers must be of low cost and suitable for mass production because large numbers of them are used in clusters in each hammermill and the life of the individual hammers is such that periodic replacement is necessary. To make it feasible to shape the individual hammers by inexpensive shearing and punching operations, steel stock not exceeding inch thick is used and the hammers are commonly provided in thickness ranging from /8 inch to inch and widths not exceeding 3 inches. To provide commercially acceptable durability they must be made of shock resistant steel and should be provided with surface hardening to increase their resistance to abrasion. In hammermills, clusters of such hammers are pivota'lly suspended from a suitable support fitting in an opening in each hammer near one end so that the other end port-ion of the hammer is subject, when in use, to severe abrasive and shock forces directed longitudinally of the working end portion of the hammer. The positions of the hammers in the mill are changed from time to time when the wear at any corner or end portion has progressed to a degree where the hammer becomes inefhcient or ineffective to perform its normal function.

Efficient operation is promoted by providing hard faces on the end surfaces of the hammers. After a period of use the hard face becomes undercut so that it forms a sharp striking edge which increases the rate of grinding or crushing of the material treated in the hammermill. Heretofc-re the effectiveness of such hard facing material has been seriously limited due to the difiiculties attendant upc-n applying such material in sulficient quantity and in fusing it to the steel hammer body with sufficient strength to prevent the spalling or breaking away of the hardening material under the forces tending to dislodge it even before the face hardening has been undercut in normal use.

It is, therefore, an object of my invention to provide in a hammer of the class described a hard face of increased thickness and greatly improved durability and resistance to shock, adapted to be applied in molten condition to the body of the hammer at low cost.

A particular object is to provide a working face portion of such a hammer comprising a relatively thick body of extremely hard, abrasion resistant material which interlocks with a series of reinforcing steel teeth projecting from the base or body of the hammer whereby the area of fusion between the face hardening mate-rial and the base is greatly extended, the useful life of the hammer is greatly increased and greatly increased resistance to impact forces directed longitudinally of the working face and acrossways of the teeth is obtained.

A further object is to provide a novel low cost method of building up hard faces of the character described on steel hammermill hammers of flat, generally rectangular shape and thickness suitable for formation by punching or shearing operations.

The invention also includes other novel features of construction which will be more fully pointed out in the following specification and claims.

Referring to the accompanying drawings:

FIGURE 1 is a perspective view showing a hammermill hammer embodying my invention, one corner portion of the hammer being shown worn away as after a period of use;

FIG. 2 is a perspective view showing a modification of the improved hammer;

FIG. 3 is a similar view showing another modification;

FIG. 4 is a plan view showing fragmentary end portions of adjoining hammers after a length of steel bar stock has been severed by a typical punching operation to form teeth on the ends of the hammer bodies, and

FIG. 5 illustrates, diagrammatically, my preferred method for applying and building up molten hardening material on a multiplicity of hammer bodies held in a suitable fixture.

Referring to FIG. 1, my improved hammer has a steel body 6 of suitable thickness and generally rectangular form. Extending through this body at suitable spaced intervals along its longitudinal median line are openings 7 adapted to receive members for pivotally supporting the hammer in the mill in accordance with conventional practice. The body 6 is a short section of steel bar stock which has been cut to suitable length by a punching operation or shearing operation.

As further shown in FIG. 1, my hammer has at each end a row of teeth 8 of depth and pitch as hereinafter described. Hard face material 9 fills the spaces between the teeth 3 and extends to a level slightly above these teeth. The material 9 may be of any suitable type adapted to be applied to the working face of the hammer in molten state and to be securely fused to the entire elongated area defined by the teeth 8 and surfaces between them.

It will be evident that the teeth 8 interlock with the material and greatly increase the area of fusion with the steel body 6. By this construction I greatly increase the resistance to spalling or breaking away of the relatively hard brittle material 9 when subjected to the shock and abrasive forces which are directed longitudinally of the end surfaces of the hammer when in use. A number of hard face materials suitable for my use are known to the art. A preferred material for this use is tungsten carbide which may be applied in a molten state.

The form of the teeth 8 may be varied between wide limits, but in order to secure the advantages of the present invention the depth and pitch of these teeth in relation to the thickness of the hammer is critical within certain limits if the hammers are to be formed by economical punching or shearing operations. Thus from a practical viewpoint, the pitch, viz., the center to center spacing of the teeth along the ends of the hammer, may not be less than the thickness of the steel hammer body. Preferably the pitch is somewhat greater than the thickness of the steel body and may, without losing the entire benefits of the invention, be made as great as twice or even two and one-half times the thickness of the hammer. The depth of the teeth is also related to the pitch and thickness of the hammer. It must not exceed the pitch and is preferably approximately one-half the pitch for hammers of one-quarter inch thickness. These lower limits for the pitch and upper limits of depth of teeth are imposed by the necessity for making the hammers of fairly hard shock-resistant steel and the difficulties attendant upon punching or shearing such steel using male dies of thickness or diameter less than the thickness of the steel bar stock.

FIG. 2 illustrates a modification wherein teeth 8;: are formed with undercut sides to increase the interlocking eifect and secure maximum fusion area of the hard face material with the hammer body. MG. 3 illustrates a further modification wherein the sides of the teeth iib are substantially at right angles to the upper ends of the teeth. Since the form of the teeth is not critical, they may be cut to other suitable shapes within the spirit of my invention. In any modification, however, the proportions hereinbefore described between the pitch of the teeth and 'epth thereof in relation to the thickness of the hammer body must be maintained to secure the advantages of the present invention. The meaning of these terms pitch and depth of tooth as used herein will be further evident from FIGS. 1 and 2 wherein the pitch is indicated at l and the depth of the teeth at D.

PlG. 4 illustrates the punching operation whereby teeth are formed on the adjoining ends of each of a series of hammer bodies 6 formed from bar stock of suitable thickness. The bar stock is severed transversely by a punch die of the shape indicated at it? for the form of the invention shown in FiG. 1 thus forming teeth 8 of the required pitch and depth. Punch dies oi shapes suitable for forming the teeth of EEG. 2 and 81) of FIG. 3 will be evident from these figures taken with FIG. 4 This method of forming the individual hammer bodies is extremely economical in that it does not substantially increase the cost of the hammers as compared with a mere shearing operation forming a straight end surface on each.

To proceed with my improved method, a multiplicity of the steel hamrner bodies formed as indicated in FIG. 4 are pressed together in a suitable fixture 11 as indicated diagrammatically in FIG. 5. This futture has a cavity adapted to receive and fit a predetermined number of the hammer bodies 6 in face to face contact one with another and suitable clamping means 12; for securing them in such position that the teeth '8 on an end of each hammer body project upwardly substantially to a common horizontal plane. The hard face material 9 is then applied in molten state quickly and easily to the entire group of hammer bodies. An oxygen-acetylene flame may be used to wet the end surfaces or" the hammer bodies by heating the steel to a critical temperature and then at that instant a suitable molten hard surfacing compound is applied. Such a compound may be melted by the use of an oxygen-acetylene flame.

An example of suitable procedure is indicated diagrammatically in E6. 5 wherein it is assumed that flame heads 13 and 14 are movable horizontally across and a ove the upper ends of the hammer bodies 6 held in the fixture 11. These heads are supplied with suitable gaseous fuel through tubes i5 and are formed to direct high temperature flame and face material respectively upon the toothed surfaces of the hammer bodies. The preheating function is performed by flame from head 14 while molten hard face material 9 is fed from the head i3. Rods 3.6 of such material are fed into the head l3, as required, so that proper distribution of the molten material 9* proceeds rapidly and continuously until the desired thick- :ness of such material has been built-up. in this manner the level of the hard surface material is built-up to an elevation slightly above the upper'ends of the teeth 8. The surface tension of the molten material makes this feasible. After the hard face material has solidified, the several hammer bodies of the group are separated by suitable means. This may require the application ofliorce as by the use of a chisel to break them apart in planes such as those indicated by brolgen lines 9;; in FIG; 5. Th

greatly increased thickness of the hardening material thus obtainable is in part the result of the resistance offered by the teeth on the hammer bodies to lateral flow of the molten material.

The effect of a period of use of my improved hammer is illustrated H6. 1 wherein one corner portion of the hammer is shown worn away at 17 so that there is a sharp cutting edge 38 presented or impact with the material in the mill. Thorough tests and extensive commercial operations have demonstrated that, as compared with co ven-tional hammers, the life of my improved hammers is greatly increased, their efficiency in operation is greatly improved and they have much improved resistance to the breaking away of the hard face material from the shockresistant steel bodies of the hammers.

The present application is a division of my application Serial No. 712,732, filed February 3, 1958, for Surface Hardening for Hammer-mill Hammers and Method of Forming the Same.

l claim:

1. A method of building up hard faces on the ends of steel hammermill bodies which comprises, forming on end portion of each body a row of teeth of sub stan.. l pitch and depth extending crosswise of the end thereof with t .e tops of the teeth in a common plane, pressing a multiplicity of said bodies in face to face contact one with another in a group, supporting said group with the teeth projecting upwardly substantially to a common level, heating the exposed surfaces of said teeth to the critical temperature of said steel bodies while filling the spaces between the teeth to an elevation above the upper ends of the teeth with a molten face hardening mat rial, whereby to cause fusion of such face hardening material to the entire end surfaces or" the several hammer bodies defined by said teeth including the surfaces between the teeth, and separating the several individual hammermill bodies one drom the others when the hard facing material has solidified.

2. A method of building up hard faces on flat steel hammenmill bodies which comprises, cutting elongated steel bar stock into a multiplicity of individual hammer bodies by a series of punching operations whereby a row of teeth of substantial pitch and depth extending crosswise of the end thereof with the tops of the teeth in a common plane is formed on each hammer body, pressing a multiplicity of said bodies in face to race contact one with another as a group, supporting said group with the teeth projecting upwardly substantially to a common elevation, heating the exposed surfaces of said teeth to the critical temperature of said steel bodies while filling the spaces between the teeth to an elevation above their upper ends with a molten face hardening material, whereby to cause the fusion of such hardening material to the entire end surfaces or" the several hammer bodies defined by said teeth and the surfaces between them, and separatthe individual hammer bodies one from the others when the face hardening material has solidified.

3. A method of building up herd faces on the ends of flat steel hammermill bodies in accordance with claim 1 wherein said hard facing material comprises tungsten carbide.

References Qited in the file of this patent UNITED STATES PATENTS 2,468,816 Duce May 3, 1 49 

1. A METHOD OF BUILDING UP HARD FACES ON THE ENDS OF FLAT STEEL HAMMERMILL BODIES WHICH COMPRISES, FORMING ON AN END PORTION OF EACH BODY A ROW OF TEETH OF SUBSTANTIAL PITCH AND DEPTH EXTENDING CROSSWISE OF THE END THEREOF WITH THE TOPS OF THE TEETH IN A COMMON PLANE, PRESSING A MULTIPLICITY OF SAID BODIES IN FACE TO FACE CONTACT ONE WITH ANOTHER IN A GROUP, SUPPORTING SAID GROUP WITH THE TEETH PROJECTING UPWARDLY SUBSTANTIALLY TO A COMMON LEVEL, HEATING THE EXPOSED SURFACES OF SAID TEETH TO THE CRITICAL TEMPERATURE OF SAID STEEL BODIES WHILE FILLING THE SPACES BETWEEN THE TEETH TO AN ELEVATION ABOVE THE UPPER ENDS OF THE TEETH WITH A MOLTEN FACE HARDENING MATERIAL, WHEREBY TO CAUSE FUSION OF SUCH FACE HARDENING MATERIAL TO THE ENTIRE END SURFACES OF THE SEVERAL HAMMER BODIES DEFINED BY SAID TEETH INCLUDING THE SURFACES BETWEEN THE TEETH, AND SEPARATING THE SEVERAL INDIVIDUAL HAMMERMILL BODIES ONE FROM THE OTHERS WHEN THE HARD FACING MATERIAL HAS SOLIDIFIED. 